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United States Patent |
5,539,140
|
Davidovits
|
July 23, 1996
|
Method for obtaining a geopolymeric binder allowing to stabilize,
solidify and consolidate toxic or waste materials
Abstract
The method of the invention provides a geopolymeric binder in powder, used
for the ultra rapid treatment of materials, soils or mining tailings,
containing toxic wastes. Said geopolymeric binder has a setting time equal
to or greater than 30 minutes at a temperature of 20.degree. C. and a
hardening rate such as to provide compression strengths (Sc) equal to or
greater than 15 MPa, after only 4 hours at 20.degree. C., when tested in
accordance with the standards applied to hydraulic binder mortars having a
binder/sand ratio equal to 0.38 and a water/binder ratio between 0.22 and
0.27. The preparation method includes the following three reactive
constituents:
a) an alumino-silicate oxide (Si.sub.2 O.sub.5, Al.sub.2 O.sub.2) in which
the Al cation is in (IV-V) coordination as determined by MAS-NMR
analytical spectroscopy for .sup.27 Al;
b) a disilicate of sodium and/or potassium (Na.sub.2.K.sub.2)(H.sub.3
SiO.sub.4).sub.2 ;
c) a silicate of calcium
where the molar ratios between the three reactive constituents being equal
to or between
##EQU1##
where Ca.sup.++ designates the calcium ion belonging to a weakly basic
silicate of calcium whose atomic ratio Ca/Si is lower than 1.
Inventors:
|
Davidovits; Joseph (16 rue Galilee, Saint Quentin, FR)
|
Appl. No.:
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855633 |
Filed:
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May 1, 1992 |
Foreign Application Priority Data
Current U.S. Class: |
588/3; 106/607; 106/624; 588/9; 588/10 |
Intern'l Class: |
G21F 009/00 |
Field of Search: |
106/607,624
588/3,9,10
|
References Cited
U.S. Patent Documents
4028454 | Dec., 1977 | Davidovits et al. | 264/82.
|
4349368 | Aug., 1982 | Davidovits | 106/84.
|
4377415 | Jun., 1983 | Johnson et al. | 524/4.
|
4472199 | Aug., 1984 | Davidovits | 106/813.
|
4509985 | Mar., 1985 | Davidovits et al. | 106/624.
|
4537710 | Aug., 1985 | Komarneni et al. | 252/631.
|
4640715 | Feb., 1987 | Heitzmann et al. | 106/706.
|
4642137 | Feb., 1987 | Heitzmann et al. | 106/607.
|
4842649 | Jan., 1989 | Heitzmann et al. | 106/707.
|
4859367 | Apr., 1989 | Davidovits | 252/628.
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5114622 | Apr., 1992 | Funabashi et al. | 252/629.
|
Other References
D. C. Comrie et al. "Geopolymer Technologies in Toxic Waste Management",
Geopolymer '8, vol. 1, pp. 107-123, Universite de Technologie, Compiengne,
France, (1988).
Davidovits et al. "Long Term Durability of Hazardous Toxis and Nuclear
Waste Disposals." Geopolymer '88, vol. 1, pp. 125-134, Universite de
Technologie, Compiegne, France, (1988).
Sang et al., "Aluminum-27 and Silicon-29 MAS-NMR Study of the
Kalinite-Mullite Transformation," J. Am. Cearm. Soc., 71 (10, C418-C421
(1988).
Regourd, "Microanalytical Studies of Surface Hydration Reactions of Cement
Compounds." Phil. Tran. R. Soc. Lond. A 310, 85-92 (1983).
Skibsted, "High-speed .sup.29 SI and .sup.27 AL MAS NMR Studies of Portland
and High Alumina Cements," Geopolymer '88, vol. 3, pp. 179-194, Universite
de Technologie, Compiegne, France 1988.
MacKenzie et al., "Outstanding Problems in the Kaolinite-Mullite Reaction
Sequence Investigated by .sup.29 Si and .sup.27 Al Solid State NMR", J.
Am. Cearm. Soc., 68 (6), 293-297 (1985).
|
Primary Examiner: Walsh; Donald P.
Assistant Examiner: Chi; Anthony
Attorney, Agent or Firm: Browdy and Neimark
Claims
I claim:
1. A method for preparing a geopolymeric binder in powder, used for the
ultra-rapid treatment of materials, soils or mining tailings containing
toxic wastes, wherein said geopolymeric binder being obtained from a
powdered mineral geopolymeric composition containing the following three
reactive constituents:
a) an alumino-silicate oxide (Si.sub.2 O.sub.5,Al.sub.2 O.sub.2) in which
the Al cation is in (IV-V) coordination as determined by MAS-NMR
analytical spectroscopy for .sup.27 Al;
b) a disilicate of sodium and/or potassium (Na.sub.2,K.sub.2)(H.sub.3
SiO.sub.4).sub.2 ;
c) a silicate of calcium
where the molar ratios between the three reactive constituents being equal
to or between
##EQU4##
where Ca.sup.++ designates the calcium ion belonging to a weakly basic
silicate of calcium whose atomic ratio Ca/Si is lower than 1.
2. A method according to claim 1) wherein said weakly basic silicate of
calcium whose Ca/Si atomic ratio is lower than 1, being obtained in the
naissant state by alkaline attack on a basic anhydrous silicate of calcium
whose atomic ratio Ca/Si is equal to or greater than 1, which generates in
situ a hydrated silicate of calcium whose atomic ratio Ca/Si is equal to
0.5 as in the disilicate Ca(H.sub.3 SiO.sub.4).sub.2 or between 0.5 and 1
as for example in tobermorite, Ca.sub.10 (Si.sub.12
O.sub.31)(OH).sub.6,8H.sub.2 O, as determined by the Ca.sub.2p /Si.sub.2p
ratio using XPS (X-ray photoelectronic spectroscopy).
3. A method according to claim 1) wherein said alkaline disilicate being
the disilicate of potassium, K.sub.2 (H.sub.3 SiO.sub.4).sub.2, the
geopolymeric binder corresponds to the formation of a geopolymer of the
type (Ca,K)-poly(sialate-siloxo) of formula varying between
(0.6K+0.2Ca)(--Si--O--Al--O--Si--O--), H.sub.2 O and
(0.4K+0.3Ca)(--Si--O--Al--O--Si--O--), H.sub.2 O.
4. A method according to anyone of claims 1, 2, 3, wherein after hardening
has taken place, the Al cation being entirely in (IV)-fold coordination as
determined by MAS-NMR analytical spectroscopy for .sup.27 Al, and the
degree of polymerization of SiO.sub.4 tetrahedra being (Q.sub.4) as
determined by MAS-NMR spectroscopy for .sup.29 Si.
5. A method for preparing a geopolymeric binder according to anyone of
claims 1, 2, 3, wherein said basic anhydrous silicate of calcium is in
solid solution with an aluminate of calcium or an alumino-silicate of
calcium In which the Al cation Is in (IV) coordination, and said
alumino-silicate oxide (Si.sub.2 O.sub.5,Al.sub.2 O.sub.2) having the Al
in (IV-V) coordination is mixed with natural or artificial aluminous
(Al.sub.2 O.sub.3) or silico-aluminous (nSiO.sub.2 Al.sub.2 O.sub.3)
powders in which the Al cation is in (VI) coordination, characterized
hereby that, after hardening, the ratio between the concentration of Al
cation in coordination (IV) and the concentration of Al cation in
coordination (VI), being:
Al(IV)/Al(VI) equal to or greater than 1 as determined by MAS-NMR
spectroscopy for .sup.27 Al, and the ratio between the SiO.sub.4 (Q.sub.4)
tetrahedra and the concentration of SiO.sub.4
(Q.sub.0)+(Q.sub.1)+(Q.sub.2) tetrahedra being:
(Q.sub.4)/[(Q.sub.0)+(Q.sub.1)+(Q.sub.2)] equal to or greater than 1 as
determined by MAS-NMR analytical spectroscopy for .sup.29 Si.
6. A method for preparing a mineral geopolymeric composition according to
claim 2, wherein said basic silicate of calcium whose atomic ratio is
equal to or greater than 1, being selected from wollastonite,
Ca(SiO.sub.3), gehlenite, (2CaO.Al.sub.2 O.sub.3.SiO.sub.2) and akermanite
(2CaO.MgO.2SiO.sub.2).
7. A geopolymeric compound, in powder, used for the ultra-rapid treatment
of materials, soils or mining tailings containing toxic wastes,
comprising:
a) 100 parts by weight of alumino-silicate oxide (Si.sub.2 O.sub.5,Al.sub.2
O.sub.2) having the Al cation in (IV-V) fold coordination as determined by
MAS-NMR analytical spectroscopy for .sup.27 Al, and
b) 48-72 parts by weight of potassium disilicate (K.sub.2 (H.sub.3
SiO.sub.4).sub.2 and
c) 50-70 parts of vitreous basic silicate, composed partly of gehlenite,
akermanite and wollastonite.
8. A geopolymeric compound according to claim 7) wherein said 48 to 72
parts of potassium disilicate K.sub.2 (H.sub.3 SiO.sub.4).sub.2 powder
being replaced by a mixture containing
35-40 parts of potassium silicate K.sub.2 O,3SiO.sub.2, 3H.sub.2 O
7-15 parts of potassium hydroxide KOH, 90% anhydrous
0-65 parts of amorphous silica.
9. A geopolymeric compound in powder, used for the ultra-rapid treatment of
materials, soils or mining tailings containing toxic wastes, comprising:
a) 100 parts by weight of alumino-silicate oxide (Si.sub.2 O.sub.5,
Al.sub.2 O.sub.2) having the Al cation in (IV-V) coordination as
determined by MAS-NMR analytical spectroscopy for .sup.27 Al, and
b) 42-64 parts of sodium disilicate Na.sub.2 (H.sub.3 SiO.sub.4).sub.2 and
c) 50-70 parts of vitreous basic silicate, composed partly of gehlenite,
akermanite and wollastonite.
Description
This invention relates to a method for solidifying and disposing waste,
particularly solidifying and disposing wastes which are harmful or
potentially harmful to man or the natural environment.
In recent years, considerable attention has been directed to the problem of
long term disposal of wastes, particularly wastes which are toxic,
radioactive or otherwise incompatible with the natural environment. Such
wastes are major by-products of the mining, chemical, petroleum, atomic
energy and other industries.
In this specification, the term "waste" refers exclusively to a waste
product containing toxic products which are harmful to man or to the
natural environment. The term "waste stabilization" refers to the chemical
conversion of toxic components into a chemical form that is stable and
resistant to the leaching of natural waters.
The term "waste solidification" refers to the transformation of a liquid,
pasty, semi-solid waste into a cohesive monolithic resistant solid.
In the mining industry, for example, typically huge amounts of gangue
minerals must be mined with the ore. The gangue is usually separated from
the ore at a mill close to the mine site and is disposed locally,
generally in so-called "tailings impoundments". These impoundments are
subject to weathering and ground Water seepage, leaking into the
surrounding environment. Tailings impoundments from non-metallic mines,
such as potash mines, frequently have significant sak concentrations which
may be leached over time resulting in high chloride concentrations in
surrounding water tables. Tailings impoundments of coal mines and many
metallic mines often have high sulphide contents. Weathering and
subsequent oxidation can produce sulphuric acid, which seeps into the
environment, leaching and carrying toxic heavy metals with it.
Conventional inorganic binders are generally used for the stabilization of
soils and tailings contaminated with toxic wastes. Yet, these inorganic
binders have very limited properties. Portland cement, for example,
soluble silicate based and lime based binders (pozzolanic binders) are
chemically incompatible for solidification of various wastes, particularly
those containing: sodium salts of arsenate, borate, phosphate, iodate and
sulfides; salts of magnesium, tin, zinc, copper and lead; silts and clays;
coal and lignite. Their solidified wastes do not remain stable for a long
time and are easily deteriorated with acidic infiltrations. Heavy
concentrations in oxidized sulfides are destroying the solidified
disposal, and accelerate the degradation and the leaching of the hazardous
elements.
Inorganic binders which are well adapted to the stabilization and
solidification of toxic wastes are pertaining to the geopolymeric type of
binders, poly(sialate) and poly(sialatesiloxo). Thus, Davidovits Patent
(U.S. Pat. No. 4,859,367; PCT WO 89/02766) provides a method for
solidifying and disposing of wastes having archaeological long term
durability. This method provides solidification and disposal for wastes
which are harmful or potentially harmful to man or the natural
environment. The method disclosed In U.S. Pat. No. 4.859,367 comprises the
steps of preparing an alkali alumino-silicate geopolymer binder, mixing
said binder with said toxic and hazardous waste in proportion such that a
mixture Is made having in situ a geopolymeric matrix of the poly(sialate)
(--Si--O--Al--O--) and/or poly(sialate-siloxo) (--Si--O--Al--O--Si--O--)
and/or poly(sialate-disiloxo) (--Si--O--Al--O--Si--O--Si--O--) types, said
geopolymeric matrix providing simultaneously the stabilization of said
toxic elements and the solidification of said waste to produce a solid and
stable material: long term stability is provided when, in the geopolymeric
matrix, the molar ratio of oxides Al.sub.2 O.sub.3 : M.sub.2 O is in the
range of 1,5 to 4,0, where M.sub.2 O is Na.sub.2 O or K.sub.2 O or the
mixture Na.sub.2 O+K.sub.2.
The leachate extraction procedure used In the present Invention follows
Regulation 309, Revised Regulations of Ontario, 1980. as amended to O.Reg.
464/85, under the Environmental Protection Act, November, 1985, according
to:
a 50 g aliqot of pre-ground sample was placed In a 1000 ml polypropylene
bottle and 800 ml deionized water added. After fifteen minutes extraction
on a rotary tumbler (14 rpm), the solution pH was measured and quantities
of 0.5 N acetic acid (or hydrochloric acid) added to bring the pH to 5.0.
The rotary extraction was continued with adjustments to pH 5.0 as
necessary, at intervals of one, three, six, and twenty-two hours. At the
end of twenty-four hours of extraction, the total volume of liquid added
was made to 1000 ml with deionized water and the final pH recorded. The
extract was filtered through 0.45 micron membrane. The leachate (filtrate)
was analyzed for trace metals by DC plasma emission spectrophotometry.
On the contrary leaching tests carried out In the prior art Involved no
acidic conditions at all, very low leaching times and partial or no
stirring of the samples.
The Leaching Procedure used in U.S. Pat. No. 4,116,705 (Chappell), Sep. 26,
1978 is outlined in col. 4, lines 11-16:
The "leachate" is the solution produced by grinding 10 g. of the hard
rock-like material produced from the slurry Into a fine powder and
stirring with 100 ml. of distilled water at 20.degree. C. for 1 hour In a
magnetically stirred vessel and filtering through a Warman No. 1 filter
paper, unless otherwise stated.
The leaching tests used in German Patents DE 24,26,641 (Chappell) and DE
29,44,484 (Chappell) follow the same leaching procedures as described in
U.S. Pat. No. 4,116,705 above. In the leaching test carried out In German
Patent DE 26,34,839, 903 of the rock-like material are immersed In 900 ml
of water at room temperature for 72 hours, without any stirring.
It is obvious that the pollutants which have not leached out from the
hard-rock like product, when immersed in water, would leach out of
submitted to the much aggressive conditions provided by the acidic
leaching test conducted according to Canadian Regulation 309, for at least
two reasons:
a) the solidified materials claimed in the prior art are vulnerable to
acidic solutions, and therefore would have been destroyed during the 24
hours rotary extraction test. This explains why the leaching tests of the
prior art involved only water, 1 hour stirring or no string at all.
b) After the destruction of the rock structure, the pollutants would have
become solubilized because of the low pH and would have leached out during
the 24 hours extraction. The efficiency of geopolymeric binders in toxic
waste management has been outlined in several papers, see for example J.
Davidovits & al. and D.C. Comrie & al., in Geopolymer 88, Vol. 1, Proc. of
the 1rst Conference on Soft Mineralurgy, 1988, University of Technology,
Compiegne, France). In addition to their chemical stability, geopolymeric
binders are providing early high-strength such as 30 MPa compressive
strength after 2 days. This prior art discloses also that, in the case of
arsenic treatment, the alkalis (NaOH or KOH), should be added in the form
of a solid (flakes) instead of the liquid solution which comprises regular
GEOPOLYMITE binders.
In some cases of urgency, however, there is a need for more rapid
geopolymeric binders, able to provide solidification in 30 minutes and
compressive strength as high as 15 MPa only after 4 hours at 20.degree. C.
The object of this invention is the description of such binders.
The present invention concerns a method of production of a geopolymeric
cement involved in the stabilization, solidification and disposal of toxic
wastes, providing high-early strength at room temperature. More
specifically the inorganic compositions described in this invention enable
production of a geopolymeric cement with a setting time equal to or
greater than 30 minutes at a temperature of 20.degree. C. and a hardening
rate such as to provide compression strengths (Sc) equal to or greater
than 15 MPa, after only 4 hours at 20.degree. C., when tested in
accordance with the standards applied to hydraulic binder mortars having a
binder/sand ratio equal to 0.38 and a water/binder ratio between 0.22 and
0.27.
The geopolymeric inorganic compositions according to the present invention
giving, rapid hardening geopolymeric cement, (Sc)>15 MPa at 4h-20.degree.
C., involve basically three reactive constituents.
The first reagent is an alumino-silicate oxide (Si.sub.2 O.sub.5, Al.sub.2
O.sub.2) in which the Al cation is in (IV-V) fold coordination as
determined by MAS-NMR spectrography for .sup.27 Al: this aluminosilicate
oxide (Si.sub.2 O.sub.5, Al.sub.2 O.sub.2) is obtained by thermal
treatment in an oxidizing medium of natural hydrated alumino-silicates, In
which the cation Al is in (VI)-fold coordination as determined by MAS-NMR
spectrography for .sup.27 Al. In the previous patents filed by the
inventor, the alumino-silicate oxide (Si.sub.2 O.sub.5, Al.sub.2 O.sub.2),
was defined only by Al cation in (IV)-fold coordination, this representing
the state of scientific knowledge at the time. At the present time, use of
MAS-NMR spectrography has enabled the presence of (V)-fold coordinated Al
to be confirmed. Thus the MAS-NMR spectrum shows 2 peaks, one around 50-65
ppm characteristic of 4-coordinated Al, the other around 25-35 ppm which
some workers attribute to (V)-fold coordinated Al, whereas others consider
it to be due to a deformed AI(IV) coordination. (See MacKenzie et al,
Journal of the American ceramic Society, Volume 68, pages 293-297, 1985).
We shall in what follows adopt the convention of mixed coordination
AI(IV-V) for this oxide (Si.sub.2 O.sub.5, Al.sub.2 O.sub.2).
The second reagent is a disilicate of sodium and/or potassium, soluble in
water, (Na.sub.2, K.sub.2)(H.sub.3 SiO.sub.4).sub.2 ; it is preferable to
use the potassium disilicate, though the sodium distillate also enables
inorganic geopolymeric compositions according to the invention to be
produced. It is also possible to use a mixture of the two alkaline
disilicates.
The third reagent is a basic calcium silicate, i.e. one having a Ca/Si
atomic ratio equal to or greater than 1. It is essentially characterized
by its ability to germ, under alkaline attack, a weakly basic calcium
silicate, i.e. one having a Ca/Si atomic ratio lower than 1, preferably
close to 0.5. This characterization is established using X-ray
photoelectronic spectrometry (XPS), and by determination of the Ca.sub.2p
/Si.sub.2p ratios, as indicated by M. Regourd, Phil. Trans. Royal Society,
London, A. 310, pages 85-92 (1983). In the present invention, the
preferred basic calcium silicates are vitreous gehlenite, achermanite and
wollastonite.
The inorganic compositions of the invention are also called inorganic
geopolymeric compositions, since the geopolymeric cement obtained results
from an inorganic polycondensation reaction, a so-called
geopolymerisation, unlike traditional hydraulic binders in which hardening
is the result of the hydration of aluminates of calcium and silicates of
calcium. Here too, the investigative tool used is MAS-NMR for .sup.27 Al.
The products yielded by a geopolymeric reaction, as described in the
present invention, show a single peak at 55 ppm, characteristic of Ai(IV)
coordination, whereas the hydration products obtained with traditional
hydraulic binders show a peak at 0 ppm, characteristic of Al(VI)
coordination, i.e. of the hydroxy-aluminate of calcium.
MAS-NMR spectrography of .sup.29 Si also shows a very clear difference
between geopolymers and hydraulic binders. If the degree of polymerization
of SiO.sub.4 tetrahedra is represented by Qn (n=0,1,2,3,4), distinction
can be made between monosilicates (Q.sub.0), disilicates (Q.sub.1), linear
silicate chains (Q.sub.2), grafted silicates (Q.sub.3) and silicates
forming a three-dimensional lattice (Q.sub.4). These various degrees of
polymerization are characterized in MAS-NMR spectrography of .sup.29 Si by
the following peaks: (Q.sub.0) from -68 to -77 ppm; (Q.sub.1) from -78 to
80; (Q.sub.2) from -80 to -85; (Q.sub.3) from -85 to -90; Q.sub.4 from -91
to -130 ppm. The peaks which characterize the geopolymers occur in the
region -85 to -100 ppm and correspond to the three-dimensional lattice
(Q.sub.4) which is characteristic of the poly(sialates) and
poly(sialate-siloxo). On the other hand, hydration of hydraulic binders
yielding hydrated calcium silicate C--S--H (according to the terminology
used in cement chemistry), produces peaks in the region -68 to -85 ppm
attributable either to the monosilicate (Q.sub.0)or the distillate
(Q.sub.1)(Q.sub.2); (see for example J. Hjorth, Cement and Concrete
Research, vol. 18 No.4, 1988 and J.Skibsted, Geopolymer '88, Session No.7,
Universite de Compiegne, 1988).
According to the terminology in current use for geopolymers (see for
example Geopolymer '88, Volume 1, Acres du Congres Geopolymer 88,
Universite de Technology, Compiegne, France), the rapid-setting inorganic
binder, (Sc)>15 MPa at 4h, 20.degree. C., corresponds to a geopolymer of
the type
(Ca,K)-poly(sialate-siloxo) of formula varying between
(0.6K+0.2Ca)(--Si--O--Ai--O--Si--O--), H.sub.2 O and
(0.4K+0.3Ca)(--Si--O--Al--O--Si--O--), H.sub.2 O.
There have been proposed in the past binders and cements showing rapid
setting and based on geopolymeric reactions involving the three reagents
used in the present invention.
Thus, for example, the patent Davidovits/Sawyer (U.S Pat. No. 4,509,985)
and its European equivalent EP 153,097, describe geopolymeric compositions
enabling production of rapid-setting mortars developing a compression
strength Sc=6.89 MPa after 1 hour at 65.degree. C. and Sc=41.34 MPa after
4 hours at 65.degree. C. There is also mentioned in one of the examples
from these patents a composition named "Geopolymer example II", developing
a compression strength Sc=24 MPa after 4 hours at 23-25.degree. C. From
experience acquired by workers in the field, a compression strength Sc=15
MPa after 4 hours at 20.degree. C. is equivalent to a value of Sc=22.5 MPa
after 4 hours at 25.degree. C. This composition comprises 840g of
so-called "standard" reaction mixture to which has been added, apart from
inert fillers, 220 g of ground high furnace slag. The reactive
geopolymeric constituents are characterized by the molar ratios of their
oxides:
K.sub.2 O/SiO.sub.2 0.32
SiO.sub.2 /(Al.sub.2 O.sub.3) 4.12
H.sub.2 O/(Al.sub.2 O.sub.3) 17.0
K.sub.2 O/(Al.sub.2 O.sub.3) 1.33
H.sub.2 O/K.sub.2 O 12.03
which, to enable comparison with the inorganic geopolymeric compositions of
the invention, corresponds to a geopolymeric composition of 1 mole of
alumino-silicate oxide (Si.sub.2 O.sub.5, Al.sub.2 O.sub.2), i.e. 222g,
1.12 moles of potassium disilicate, K.sub.2 (H.sub.3 SiO.sub.4).sub.2,
i.e. 300 g, 0.21 moles of K.sub.2 O corresponding to 28 g of 90% anhydrous
KOH, 290 g of water and 220 g of slag.
Compared with the alumino-silicate oxide (Si.sub.2 O.sub.5, Al.sub.2
O.sub.2) in the composition described in U.S. Pat. No. 4,509,985, the
molar ratio of K.sub.2 (H.sub.3 SiO.sub.4).sub.2 to (Si.sub.2 O.sub.5,
Al.sub.2 O.sub.2) is easily seen to be 1.12.
The greatest contribution to the price of inorganic geopolymeric
compositions is that of the potassium distillate K.sub.2 (H.sub.3
SiO.sub.4).sub.2. It was thus very important to find a way of
substantially reducing the quantity of this very costly substance. This is
the main objective of the present invention.
In the terms of the invention, inorganic geopolymeric compositions are
characterized by the molar ratios between the three reactive constituents
which are equal or between
##EQU2##
where Ca.sup.++ represents the calcium ton belonging to a weakly basic
silicate of calcium. As can be seen, the quantity of alkaline disilicate
is reduced by 200% to 300% compared to the quantity previously required.
To achieve this, it is not in fact sufficient simply to reduce the quality
of this alkaline disilicate: the inventor was surprised to realize that
what was essentially necessary, was to change the physical state of the
constituents.
Thus, the compositions of the Davidovits/Sawyer U.S. Pat. No. 4,509,985 are
in the liquid phase. The slag is added to an aqueous reaction mixture
containing the alumino-silicate oxide (Si.sub.2 O.sub.5,Al.sub.2 O.sub.2),
the alkalis the water and the potassium polysilicate in solution.
In contrast, in this invention, the inorganic geopolymeric compositions are
in the solid phase, in particular the second reactive constituent, the
sodium and/or potassium disilicate (Na.sub.2,K.sub.2)(H.sub.3
SiO.sub.4).sub.2 is in the form of a finely divided powder, the water only
being added in the final phase of mixing the mortar or binder.
Inorganic powder compositions are also in the technique In its previous
state. Thus the U.S. Pat. No. 4,642,137 (Heitzmann) claims inorganic
compositions containing:
100 parts of metakaolin
20 to 70 parts of slag
85 to 130 parts of fine fillers (light ashes, calcinated clays).
70 to 215 parts of amorphous silica
55 to 145 parts of a mixture containing potassium silicate and potassium
hydroxide, with a minimum of 55 parts of potassium silicate.
As indicated in Heitzmann's U.S. Pat. No. 4,642,137, the amorphous silica
essentially has the role of replacing part of the potassium silicate
necessary for the geopolymerisation. i.e. the amorphous silica reacts:
with potassium hydroxide to produce, in the mortar, the required quantity
of potassium silicate. For workers in the field, the term "potassium
silicate" used in Heitzmann's U.S. Pat. No. 4,642,137 means industrial
potassium silicate in the form of a powder, corresponding to the formula
K.sub.2 O.SiO.sub.2.3H.sub.2 O, soluble in water and enabling the
production of binders and adhesives ha,ring the same properties as
`soluble glasses` or alkaline silicates in solution.
However, these formulations according to Heitzmann's U.S. Pat. No.
4,642,137 do not set at room temperature, since to obtain rapid setting it
is absolutely necessary to add portland cement. But even with the addition
of portland cement, the compositions claimed do not enable (Sc)>15 MPa at
4h-20.degree. C. Thus for the example giving the best results, example 28,
the following mixture is quoted:
68 parts of metakaolin
36 parts of slag
60 parts of light ashes
103 parts of silica powder
44 parts of potassium silicate
22 parts of potassium hydroxide and
423 parts of portland cement.
For the mortar obtained, the compression strength, Sc, after 4 hours at
23.degree. C. is 1000 PSI, i.e. only 6.9 Mpa, which is much lower than
(Sc)>15MPa at 4h_20.degree. C., as claimed in the present invention. In
another example, example 27, Sc after 4 hours at 23.degree. C. is only 680
PSI, i.e. only 4.6 MPa, while in the other examples described in U.S. Pat.
No. 4,642,137, only values of Sc at 150.degree. F. (i.e. 65.degree. C.)
are given, Sc after 4 hours at 23.degree. C. being too small to be
mentioned.
Assuming that the metakaolin corresponds to our alumino-silicate oxide
(Si.sub.2 O.sub.5,Al.sub.2 O.sub.2), and that the potassium hydroxide
afforded the transformation of potassium silicate K.sub.2
O.3SiO.sub.2.3H.sub.2 O into disilicate, K.sub.2 (H.sub.3
SiO.sub.4).sub.2, we obtain the following compositions expressed in moles:
(Si.sub.2 O.sub.5, Al.sub.2 O.sub.2) 0.30 moles
K.sub.2 (H.sub.3 SiO.sub.4).sub.2 0.20 moles
i.e. a ratio of K.sub.2 (H.sub.3 SiO.sub.4).sub.2 to (Si.sub.2 O.sub.5,
Al.sub.2 O.sub.2) equal to 0.66. The ratio is actually higher since the
excess of potassium hydroxide being 0.13 moles of K.sub.2 O, as it is
claimed that this potassium has reacted with the silica powder to produce
0.13 moles of K.sub.2 (H.sub.3 SiO.sub.4).sub.2, the final total of
K.sub.2 (H.sub.3 SiO.sub.4).sub.2 is equal to 0.33 moles, giving a ratio
of K.sub.2 (H.sub.3 SiO.sub.4).sub.2 to (Si.sub.2 O.sub.5, Al.sub.2
O.sub.2) equal to 1.10, which is exactly that quoted in the
Davidovits/Sawyer U.S. Pat. No. 4,509,985 and EP 153,097 quoted above.
These examples demonstrate well that the simple replacement of the silicate
in solution by silicate in powder form causes a very substantial slowing
in the setting since, again according to Heitzmann's U.S. Pat. No.
4,642,137, thermal activation is necessary for rapid setting in a few
hours.
Now, in the present invention and contrary to previous technique, it Is
precisely the use of alkaline disilicate in powder form which enables a
geopolymeric cement to be obtained showing rapid setting, at 20.degree.
C., in a few hours, with (Sc)>15 MPa at 4h-20.degree. C.
Also quoted in the second Heitzmann U.S. Pat. No. 4,640,715 is replacement
of the whole of the potassium silicate in solution by a mixture of
amorphous silica (silica powder) and potassium hydroxide. Here too, for
rapid setting, portland cement has to be added, and in the best example,
example 43, the compression strength Sc after 4 hours at 23.degree. C. is
Sc=1100 PSI, i.e. 7.5 MPa, which is much lower than (Sc)>15 MPa at
4h-20.degree. C., as claimed in the present invention.
In this same second patent of Heitzmann, U.S. Pat. No. 4,640,715, the
geopolymeric mineral composition comprises 52 parts of metakaolin, 24 to
28 parts of potassium hydroxide, 73 to 120 parts of silica dust, 18 to 29
parts of slag. According to the description in this second patent of
Heitzmann, the silica dust reacts with the potassium hydroxide to produce,
in the mixture, potassium silicate. This is, according to Heitzmann's
second patent, a way of lowering the cost of this very expensive reagent.
We thus obtain, in moles, according to the same reasoning as above:
(Si.sub.2 O.sub.5, Al.sub.2 O.sub.2) 0.23 moles
K.sub.2 (H.sub.3 SiO.sub.4).sub.2 from 0.2 15 to 0.25 moles.
which gives a ratio of K.sub.2 (H.sub.3 SiO.sub.4).sub.2 to (Si.sub.2
O.sub.5, Al.sub.2 O.sub.2) between 0.93 and 1.08, i.e. practically equal
to the ratio discussed previously for the first patent of Heitzmann and
the Davidovits/Sawyer patent.
These examples of the previous state of the technique readily show that the
simple replacement of silicate in solution by a mixture of silica dust and
potassium hydroxide causes a very substantial slowing down in the setting,
since, according to the second patent of Heitzmann, U.S. Pat. No.
4,640,715, thermal activation is necessary to obtain rapid hardening, in a
few hours.
The examples described in the previous Heitzmann patents show that rapid
hardening requires a temperature of 40.degree.-60.degree. C. In other
words, the mixtures claimed are endothermic; they absorb heat.
The following tests demonstrate that-In the previous state of the
technique, the endothermicity of the mixtures was too high for rapid
hardening at room temperature. It is known that the geopolymerisation
reaction, as described in the Davidovits patents U.S. Pat. No. 4,349,386
(FR 2.464.227) and U.S. Pat. No. 4,472,199 (FR 2.489.290), is exothermic,
this exothermicity being very obvious when hardening is carried out at
40.degree.-60.degree. C. The exothermicity of mixtures with and without
amorphous silica, such as silica dust, has been measured.
The technique used was differential thermal analysis.
Two powder mixtures are prepared:
powder A: oxide (Si.sub.2 O.sub.5,Al.sub.2 O.sub.2) 400 g
micronised mica 100 g
powder B: oxide (Si.sub.2 O.sub.5, Al.sub.2 O.sub.2) 400 g
silica dust 100 g
and 2 liquid mixtures:
liquid 1: potassium silicate, 40% solution 520 g
KOH, 90% 82 g
liquid 2: sodium silicate solution, 40% 1040 g
NaOH powder 120 g
Mixing of powder and liquid is carried out according to the proportions
indicated in the table, and the geopolymerisation is followed by
differential thermal analysis. Values of the ratio J/g are compared, i.e.
the mount of energy, measured in Joules divided by the mass of the sample
in grammes. The geopolymerisation temperature is 60.degree. C.
______________________________________
Test No. Mixture J/g
______________________________________
1 powder A 55 g 247
liquid 1 100 g
2 powder B 55 g 53
liquid 1 100 g
3 powder B 55 g 116
liquid 2 100 g
______________________________________
It can clearly be seen that the addition of silica dust, i.e. the formation
of potassium silicate in the mixture, causes thermal energy to be
absorbed. The exothermicity of test No. 2 (with silica dust) is five times
less than that of test No. 1 (without silica dust), and that of test No. 3
is half that of test No. 1.
This is the explanation given for why the mixtures claimed in the patents
of Heitzmann do not set rapidly at room temperature.
On the other hand, in the present invention, the amorphous silica, such as
silica dust, or other silicas which are known to transform readily into
potassium or sodium silicate at moderate temperatures, or even room
temperature, is added in such an amount that it does not perturb the
natural exothermicity of the geopolymeric mixture. Amorphous silica, such
as for example silica dust, rice ashes, diatomaceous earths,, silicic
smectites, certain highly silicic pouzzolanes (with a high percentage of
allophane and glass of volcanic origin) are considered as finely divided
reactive fillers. The reactivity of these fillers makes them react on the
surface with the geopolymeric reactive medium, thus increasing the
mechanical strength of the poly(sialate-siloxo) mineral binder. These
silicic materials are not at first dissolved, at ordinary temperatures,
i.e. in the terms of reference of this invention. However, as in the case
of hydraulic binders which contain them, it is possible, after not more
than 28 days, to observe that they have been digested by the geopolymeric
matrix or by the basic silicates still present in the matrix.
The third reactive constituent of the invention is weakly basic calcium
silicate with a Ca/Si ratio lower than 1.
This could typically be calcium disilicate Ca(H.sub.3 SiO.sub.4).sub.2 or
tobermorite Ca.sub.10 (Si.sub.12 O.sub.31)(OH).sub.6, 8H.sub.2 O. The
amount of this third reactive constituent is linked to the other ones by
the mole ratios between the three reactive constituents being equal to or
within
##EQU3##
In the cases of calcium disilicate Ca(H.sub.3 SiO.sub.4).sub.2 and
potassium disilicate K.sub.2 (H.sub.3 SiO.sub.4).sub.2 the mole ratios are
equal or between
K.sub.2 (H.sub.3 SiO.sub.4).sub.2 /(Si.sub.2 O.sub.5, Al.sub.2 O.sub.2)
0,40 and 0,60
Ca(H.sub.3 SiO.sub.4).sub.2 /(Si.sub.2 O.sub.5, Al.sub.2 O.sub.2) 0,60 and
0,40
In other words, the sum of the number of moles of calcium disilicate
Ca(H.sub.3 SiO.sub.4).sub.2 and the number of moles of potassium
disilicate K.sub.2 (H.sub.3 SiO.sub.4).sub.2, is equal to the number of
moles of alumino-silicate oxide (Si.sub.2 O.sub.5, Al.sub.2 O.sub.2). This
alumino-silicate oxide (Si.sub.2 O.sub.5, Al.sub.2 O.sub.2) determines all
the reaction conditions of the geopolymeric mineral compositions. It
reacts with alkali or alkaline-earth disilicates to form, after
geopolymerisation, a compound [Si.sub.2 O.sub.5,Al.sub.2 O.sub.2, Si.sub.2
O.sub.5, (K.sub.2 O, CaO)]-poly(sialate-siloxo), i.e. of formula between
(0.6K+0.2Ca)(--Si--O--Al--O--Si--O--) and
(0.4K+0.3Ca)(--Si--O--Al--O--Si--O--)
The oxide (Si.sub.2 O.sub.5, Al.sub.2 O.sub.2) reacts first of all with the
most soluble disilicate, which is always the alkaline disilicate
(Na.sub.2, K.sub.2)(H.sub.3 SiO.sub.4).sub.2. The amount of calcium
disilicate taking part in the reaction is essentially determined by the
amount of alkaline disilicate. If the sum of the number of moles of these
disfiicates is greater than 1, the non-reaching part will be that which is
the least soluble, i.e. the calcium disilicate.
However, it is the calcium ions which determine the setting speed, by
making the alkaline geopolymeric gels less soluble, the optimal setting
speed being reached when the Ca.sup.++ ions are integrated into the
geopolymeric structure. If the amount of alkaline Na.sup.+ or K.sup.+ is
large, a larger amount of Ca.sup.++ ion will be necessary to obtain the
same setting speed. On the other hand, of the amount of alkaline
disilicate, (Na.sub.2, K.sub.2)(H.sub.3 SiO.sub.4).sub.2, is too small,
the dissolution of calcium disilicate, Ca(H.sub.3 SiO.sub.4).sub.2, will
be reduced, rapid setting at 20.degree. C. will not occur, and mechanical
strengths will be lower.
This could be the explanation given for the Heitzmann patents for which the
ratio K.sub.2 (H.sub.3 SiO.sub.4).sub.2 /(Si.sub.2 O.sub.5, Al.sub.2
O.sub.2) was close to or greater than 1, as to why the too high solubility
of the reaction medium slowed down the precipitating action of the
Ca.sup.++ ions originating from, for example, slag or portland cement.
Calcium disilicate, Ca(H.sub.3 SiO.sub.4).sub.2, can be manufactured
separately, for example by hydrothermal reaction between lime and silica.
However, according to a method preferred in the invention, it will be
produced in a naissant state in the binder after addition of the water
required for solubilising the various powder reagents. The starting
material is a basic calcium silicate, i.e. with a Ca/Si-atomic ratio equal
to or greater than 1. Hydratation should not produce compounds containing
free lime (CaO) or Ca(OH).sub.2, which are very sensitive to acidic
attack, these compounds resulting generally during hydratation of Portland
cement components, bicalcic silicate (2CaO.SiO.sub.2) and tricalcic
silicate (3CaO,SiO.sub.2). On the other hand, other basic silicates such
as wollastonite, Ca(SiO.sub.3), gehlenite, (2CaO.Al.sub.2 O.sub.3
SiO.sub.2), akermanite, (2CaO.MgO.2SiO.sub.2) are well adapted. When the
particles of these substances come into contact with an alkaline solution
(NaOH or KOH), very rapid desorption of CaO occurs, so that the Ca/Si
atomic ratio becomes lower than 1 and tends to 0.5 for basic silicates of
initial ratio Ca/St equal to or less than 2, such as wollastonite,
gehlenite, akermanite.
Industrial by-products contain essentially the basic silicates gehlenite,
akermanite and wollastonite, and are thus very suitable. Some examples are
vitreous high furnace slag, bottom ashes and fly-ashes produced in
high-temperature power plants. Moreover, as it can be followed by X-ray
photoelectronic spectrometry (Xps), as indicated above, this alkaline
attack on the basic silicate produces a weakly basic silicate of atomic
ratio Ca/Si=0.5, 1.e. stoichiometric calcium disilicate, Ca(H.sub.3
SiO.sub.4).sub.2. This process takes place very smoothly and can be
complete in 30 minutes at ambient temperature.
The geopolymeric reaction used In the present invention must not be
confused with simple alkaline activation of hydraulic binders, or the
action by alkalis of accelerating setting of portland cements and other
hydraulic binders.
In this respect, the simple action of alkalis, NaOH or KOH, on portland
cements or high furnace slag, results in the production of hydrated
calcium silicates, as mentioned above. Unlike what happens in the present
invention, these hydrated silicates crystallize to form C--S--H, the main
constituent of hydraulic calcium-based cements. C--S--H Is a mono and/or
disilicate, i.e. the SiO.sub.4 tetrahedra of which it is composed belong
to the categories (Q.sub.0), (Q.sub.1) and possibly (Q.sub.2). On the
other hand, geopolymerisation leads to the formation of type (Q.sub.4)
SiO.sub.4 tetrahedra, as determined by NMR MAS spectrum analysis for
.sup.29 Si. Geopolymers which are tri-dimensional alumino-silicates, are
stable to acidic attack.
Although the alkalis NaOH and KOH are setting accelerators, they are not
hardening accelerators capable of achieving the object of the invention,
namely (Sc)>15MPa at 4h-20.degree. C.
In the case of high-furnace slags, the alkalis are not setting
accelerators, but develop the latent hydraulic nature of the slags. The
hardening accelerator is in general temperature, or added portland cement,
as described for example in the patent of Forss, U.S. Pat. No. 4,306,912
which describes the use of slag-based cement, portland cement or lime, and
an alkaline accelerator such as NaOH or the carbonates of sodium or
potassium. Compression strengths are all achieved after heating at
50.degree. C. or 70.degree. C. Thus in table 4 of the patent of Forss is
found a mean Sc of 20 to 30 MPa after 6 hours at 70.degree. C. Experience
in the technique indicates that strengths of 30 MPa obtained after 6 hours
at 70.degree. C. correspond to Sc=1 to 3 MPa maximum after 4 hours at
20.degree. C.
Scientific analysis using MAS-NMR spectrography for .sup.27 Al shows that
slag-based hydraulic cements result from the hydration of calcium
aluminares, silicates and silico-aluminates, with formation either of
hydrated gehlenite, (2CaO.Al.sub.2 O.sub.3.SiO.sub.2.8H.sub.2 O), or
hydrated calcium aluminate, (4CaOAl.sub.2 O.sub.3.10H.sub.2 O), In which
the Al cation is in Al(VI) coordination. The MAS-NMR spectrum for .sup.29
Si shows the SiO.sub.4 tetrahedra to be mainly of type (Q0), (Q 1) or
(Q2), characteristic of C--S--H.
Similarly, a mixture composed of alumino-silicate oxide (Si.sub.2
O.sub.5,Al.sub.2 O.sub.2), slag and the alkalis KOH. NaOH, does not
constitute a geopolymeric mineral binder according to the present
invention. A mortar made with this mixture and water does not harden at
20.degree. C. after 4 hours. This type of reaction is described in the
previous patents of one of the inventor. Thus the patents Davidovits U.S.
Pat. No. 4,349,386 (FR 2.464.227) and U.S. Pat. No. 4,472,199 (FR
2.489.290) indicate that if the oxide (Si.sub.2 O.sub.5.Al.sub.2 O.sub.2)
is not protected by a solution of polysilicate against attack by the
strong bases KOH,NaOH, a simple poly(sialate) of the hydroxysodalite type
is formed, and is precipitated Z without any binding occurring.
Hydroxysodalite only forms a binder in ceramic pastes with very little
water and when the material is compressed, as claimed in the Davidovits
patents FR 2.346.12 1 and FR 2.341.522.
In the terms of the invention, the third reagent in the inorganic
geopolymeric mixture is calcium silicate. It may be accompanied by complex
aluminares and silicates of calcium.
Thus high furnace slag is formed partly of a glass composed amongst other
things of gehlenite, 2CaO.Al.sub.2 O.sub.3.SiO.sub.2. akermanite,
2CaO.MgO.2SiO.sub.2, and Wollastonite. In the terms of the invention, that
part of these silicates not transformed into weakly basic calcium silicate
during alkaline attack, or that part which has not taken part in the
geopolymerisation reaction once the ratio K.sub.2 (H.sub.3
SiO.sub.4).sub.2 +Ca(H.sub.3 SiO.sub.4).sub.2 to (Si.sub.2 O.sub.5
Al.sub.2 O.sub.2) has reached a value of 1, these silicates and
alumino-silicates will hydrate according to the appropriate known
mechanism for the silicates of calcium constituting hydraulic cements.
There is then obtained as well as the geopolymer
(K,Ch)(--Si--O--Al--Si--O--) the formation of hydrated gehlenite, of
C--S--H, of hydrated calcium aluminate and of other silicates of magnesia.
In opposition to pure geopolymer compounds, these hydrated compounds are
very sensitive to acid leaching. In the term of the present invention and
in order to prevent any weakness in the solidified materials, these
hydrated compounds may only be present in very small quantity. It is
therefore appropriate to remain as close as possible to the stochiometric
quantities recommended by the method of the present invention. Analysis by
MAS-NMR spectrometry for .sup.27 Al will show the presence of peaks
corresponding both to Al(IV) and Al(VI) coordination. In general, in the
terms of the present invention, the concentration of AI(IV) is 4 to 6
times higher than that of Al(VI). It can be lower of to the mixture are
added other silico-aluminous or aluminous fillers, but, even in this case,
the ratio between the concentration or Al(IV) and Al(VI) will be
Al(IV)/Al(VI) equal to or greater than 1.
In the MAS-NMR spectrum of .sup.29 Si, these same basic calcium silicates
lead to the presence of both SiO.sub.4 tetrahedra (Q.sub.4), (Q.sub.0),
(Q.sub.1), (Q.sub.2). In general the concentration of SiO.sub.4 (Q.sub.4)
is 4 to 6 times higher than the sum of the concentrations of SiO.sub.4
tetrahedra (Q.sub.O)+(Q.sub.1)+(Q.sub.2), and according to the nature of
the fillers we will have (Q.sub.4)/[(Q.sub.0)+(Q.sub.1)+(Q.sub.2)]equal to
or greater than 1.
High furnace slag is a cheap source of wollastonite, gehlenite and
achermanite. The geopolymeric mineral compositions of this invention which
contain high furnace slag enable the production of a geopolymeric mineral
binder containing:
a) 100 parts by weight or alumino-silicate oxide (Si.sub.2 O.sub.5,
Al.sub.2 O.sub.2), in which the Al cation is (IV-V) coordinated as
determined by MAS-NMR spectrometry for .sup.27 Al, and
b) 48-72 parts of potassium disilicate K.sub.2 (H.sub.3 SiO.sub.4).sub.2,
and
c) 50-70 parts of high furnace slag of average grain size 10 microns,
composed partly gehlenite, ackermanite wollastonite; the mortar obtained
by adding a quantity of water such that the water/binder ratio lies
between 0.20 and 0.27, and a quantity of normalised sand such that the
binder/sand ratio is 0.38, cold hardens and after 4 hours at 20.degree. C.
develops a compressive strength equal to or greater than 15 MPa.
Forss' patent requires a very fine grinding of the slag, in the range of
400-800 m.sup.2 /kg specific area. In opposition, in the present
invention, the grain size of the slag is in the range of 10-15 microns,
i.e. coarser, with 300 m.sup.2 /kg specific area. In the present
invention, the vitreous calcium silicates have a grain size in the range
of 10 microns, whereas the vitrified ashes already mentioned above, those
containing basic calcium silicates and produced in high-temperature power
plants, may have a smaller grain size and do not require any grinding.
When manufacturing conditions do not allow the alkaline disilicate K.sub.2
(H.sub.3 SiO.sub.4).sub.2 to be obtained directly, the 48 to 72 pars of
potassium disilicate are replaced by a powder mixture containing
35-40 parts of potassium silicate, K.sub.2 O,3SiO.sub.2,3H.sub.2 O
7-15 parts of potassium hydroxide, KOH, anhydrous to 90%
0-65 parts of amorphous silica.
The comparison between the weight ratio of slag/water enables a clear
distinction to be made between geopolymeric compositions according to the
present invention and previous knowledge. The Sawyer/Davidovits patent
indicates the limiting values of this ratio, beyond which it is no longer
possible to use the binders so produced since the mixture sets immediately
in the mixer, the setting being practically instantaneous. It should also
be noted that the formulation `Geopolymer, Example II` which uses the
maximum slag, also contains calcium fluoride CaF.sub.2. Now, it is known
that fluorides have a retarding action on the formation of weakly basic
calcium silicate, and therefore on the precipitating action of Ca.sup.++
ions, thus favourising a longer setting time, by avoiding the effect of
false setting.
On the other hand, in the terms of the present invention, setting is
considered as slow, since it takes place after a time longer than 30
minutes without addition of retarding agent, enabling it to be used In
industry with standard mixers. All workers in the field will understand
the advantage of this setting parameter of t>30 minutes at 20.degree. C.
The table shows setting times for different ratios by weight of slag/water,
of compositions involving solutions of alkaline silicate
(Davidovits/Sawyer U.S. Pat. No. 4,509,985) and geopolymeric compositions
containing powdered alkaline disilicates according to the present
invention.
______________________________________
slag/water ratio
1.0 0.85 0.70 0.55 0.42
______________________________________
start of setting
0 0 12 min
30 min
60 min
U.S. Pat No. 4,509,985
(at 73.degree. F., 23.degree. C.)
present 30 min 60 min 90 min
3 hours
invention
(at 20.degree. C.)
______________________________________
It is well known to workers in the field that the lower the amount of water
in the cement, the higher the mechanical strengths. In the prior state of
the art, the maximum slag/water ratio is 0.70. For workability, mortars
and concretes require in general minimum setting times of 30 minutes,
which, In U.S. Pat. No. 4,509,985 imposes a slag/water ratio of 0.55. But
this large amount of water causes the compression strength Sc to fall by
about 30%. On the other hand, in the present invention, the workability of
the mortar is good even with a slag/water ratio of 1.0. High mechanical
strengths are then obtained, with in addition all the other
characteristics which accompany the low quantity of water, such as, for
example, high bulk density and low porosity, and this with a reduction of
more than 200% to 300% of the most expensive constituent, the disilicate
(Na.sub.2,K.sub.2)(H.sub.3 SiO.sub.4).sub.2.
In place of potassium disilicate, K.sub.2 (H.sub.3 SiO.sub.4).sub.2, 42 to
64 parts of sodium disilicate, Na.sub.2 (H.sub.3 SiO.sub.4), can be used,
or a mixture of the two silicates. This allows use of impure alkalis
containing both potassium and sodium. This is often the case in industrial
wastes very rich in allcalls such as filter dusts from calcining ovens for
portland cement, or alkaline washings from the mining and chemical
industries.
The point of the present invention is also that use of powdered alkaline
disilicate (Na.sub.2,K.sub.2)(H.sub.3 SiO.sub.4) enables the use of cheap
raw materials from industrial wastes. A useful source of amorphous silica
is silica dust recuperated from the filters above ferro-silicon steel
fusion furnaces. These dusts contain 90-95% of SiO.sub.2, carbon, and
0.5-1% of finely dispersed silicon metal. These silica dusts enable
production of alkaline disilicate at very low or even ordinary (room)
temperatures. On the other hand, with silicious sands, it is generally
necessary to use an autoclave to make the alkaline hydroxides react, or in
fusion when alkaline carbonates are used. Naturally occurring amorphous
silica such as diatomaceous earths, smectites, highly silicious gaizes,
volcanic glasses and highly silicious pozzolans can also be used.
Silica-rich ashes, obtained by plant calcination (rice. for example), can
also be used here.
Manufacture of the alumino-silicate oxide (Si.sub.2 O.sub.5 Al.sub.2
O.sub.2) is carried out by treating kaollnitic clays between 650.degree.
C. and 800.degree. C. Kaollnitic sands can be used as raw materials, and
also some clays containing kaolinite, montmorionite and ite together; also
lateritic soils and laterites containing kaolinite. Tests carried out on
pyrophilites show them to be suitable for geopolymerisation.
Raw material thermal treatment temperatures must be controlled in such a
way that they give optimal production of alumino-silicate oxide (Si.sub.2
O.sub.5, Al.sub.2 O.sub.2) having the highest concentration of Al in
Al(IV-V) coordination as determined by MAS-NMR spectroscopy for .sup.27
Al. Silicious materials which, for technical reasons, have also to undergo
roasting, will be treated at temperatures below the temperature of
transformation of amorphous silicates into cristobalite when they are
required for use as raw material in the production of powdered alkaline
disilicate (Na.sub.2, K.sub.2)(H.sub.3 SiO.sub.4).sub.2. In general, this
temperature is close to 700.degree. C.
The alkalis are generally the hydroxides of sodium and/or potassium
manufactured industrially by electrolysis. They can also come from
chemical reaction between an alkaline salt and calcium hydroxide or a
material producing this in situ. Alkaline salts are chosen from sodium and
potassium carbonates, potassium sulphate, potassium sulphite.
The following examples are illustrative of the present invention. They in
no way reflect a limit on the overall scope of the invention as set out in
the claims. All parts are by weight.
EXAMPLE 1
Preparation of the powdered alkaline disilicate K.sub.2 (H.sub.3
SiO.sub.4).sub.2 has been carried out by us in the following way: silica
dust (130 parts by weight) is mixed with 90% KOH (125 parts); water (30
parts) is then added. After a certain time the mixture exhibits exothermic
behavior and begins to froth (action of KOH on silicon metal). It acquires
the consistency of a dough which then cools and hardens into a foamed and
very friable material. A product highly soluble in cold water is obtained,
containing 86% of dry matter and 14% of water, corresponding to technical
potassium disilicate K.sub.2 (H.sub.3 SiO.sub.4).sub.2 with 3-5% of
impurities in the form of insoluble carbon and potassium silico-aluminate.
EXAMPLE 2
Following example 2 of the Sawyer/Davidovits U.S. Pat. No. 4,509,985, a
mixture is prepared containing
222 g oxide (Si.sub.2 O.sub.5, Al.sub.2 O.sub.2),
28 g 90% KOH
to which is added a previously prepared liquid mixture containing 310 g of
powdered disilicate as in example 1) and 290 g water, followed by 220 g.
high furnace slag.
The binder thus obtained is used to make up a mortar with a binder/sand
ratio of 0.38 and in which the water/binder ratio is 0.27 .
The mortar starts to set after 15 mtns. and a compression strength Sc=16
MPa at 20.degree. C. after 4 hours.
The molar ratio K.sub.2 (HgSiO.sub.4).sub.2 /(Si.sub.2 O.sub.5,Al.sub.2
O.sub.2) is equal to 1.12 and the slag/alkaline disilicate weight ratio is
equal to 0.73 for a slag/water weight ratio of 0.75.
EXAMPLE 3
the following mixture is made:
22 parts of oxide (Si.sub.2 O.sub.5, Al.sub.2 O.sub.2)
13 parts of slag
18 parts of silica dust
36 parts of a previously prepared liquid mixture containing 12 parts of
disilicate prepared according to example 1), 4 parts of KOH and 20 parts
of water.
The mortar is made according to example 2). Setting takes place after 3
hours and Sc=2 MPa at 20.degree. C. after 4 hours.
The molar ratio K.sub.2 (H.sub.3 SiO.sub.4).sub.2 /(Si.sub.2 O.sub.5,
Al.sub.2 O.sub.2) is equal to 0.43. The slag/alkaline disilicate weight
ratio is equal to 1.08 and the slag/water weight ratio=0.65.
EXAMPLE 4
The following mixture is made:
22 parts of oxide (Si.sub.2 O.sub.5 Al.sub.2 O.sub.2)
15 parts of slag
18 parts of silica dust
40 parts of a previously prepared liquid mixture containing 15 parts of
disilicate prepared according to example 1), 4 pans of KOH and 22 parts of
water.
The mortar is prepared as In example 2). Setting takes place after 2.5
hours and Sc=4 MPa at 20.degree. C. after 4 hours, with a water/binder
ratio =0.29.
EXAMPLE 5
The following dry mixture is made:
22 parts of (Si.sub.2 O.sub.5, Al.sub.2 O.sub.2)
15 parts of slag
20 parts of silica dust
11 parts of KOH
the sand is then added, and finally 25 parts of water A mortar as in
example 2) is thus obtained. No setting takes place, even after 24 hours
at 20.degree. C.
EXAMPLE 6
The following dry mixture is made:
27 parts of (Si.sub.2 O.sub.5, Al.sub.2 O.sub.2)
21 parts of slag
15 parts of silica dust
19 parts of potassium disilicate K.sub.2 (H.sub.3 SiO.sub.4).sub.2 prepared
according to Example 1)
215 parts of normalised sand are then added followed by
21.5 parts of water.
Setting starts after 35 minutes, and the strength Sc after 4 hours at
20.degree. C. is 16 MPa, with a water/binder ratio=0.26
The molar ratio K.sub.2 (H.sub.3 SiO.sub.4).sub.2 /Si.sub.2 O.sub.5,
Al.sub.2 O.sub.2) is equal to 0.58. The slag/alkaline disilicate weight
ratio is equal to 1.10 and the slag/water weight ratio=1.023.
EXAMPLE 7
The powdered binder from Example 6 is used for the solidification and
stabilization of mining tailings which contain heavy metals like those
described in the Example 1) of Davidovits U.S. Pat. No. 4,859,367,
according to following process:
32.5 kg of tailings are blended with 50 kg of sand, and 17.5 kg of the
binder of Example 6. After mixing, water is added to the blend providing a
ratio water/binder lower than 0.27. The mortar obtained is then cast into
molds and vibrated to remove entrained air. The test-bars harden within 35
minutes at ambiant temperature. After 4 hours of cure at 20.degree. C. the
compressive strength Sc is 15 MPa.
The samples are tested according to the acidic leachate procedure, Canadian
Regulation 309 as stated here above. All toxic elements have been locked
within the geopolymeric framework.
EXAMPLE 8
25 kg supplementary binder of Example 6 are added to the blend of Example
7. The sample hardens under the conditions set forth in Example 7 and have
a compressive strength of 25-30 MPa (3700-4400 PSI) after 4 hours cure at
20.degree. C. This strength is identical to the compressive strength
disclosed In the prior art of D.C. Comrie and al. for GEOPOLYMITE binders,
but where the cure is carried out during 48 hours. This strength is also
equivalent to the compressive strength disclosed in Example 2) of
Davidovits U.S. Pat. No. 4,859,367, with GEOPOLIMITE binders, but after
curing at 60.degree. C. for 4 hours and subsequent hardening during 14
days.
Workers in the field will understand how important it can be to have a
method which allows the ultra-rapid stabilization of sites contaminated
with toxic elements. Due to the high early strength, the part of the soil
stabilized and solidified according to the method set forth in the present
invention can deal as access way for heavy motorized trucks, within only 2
to 3 hours after solidification took place.
Naturally, various modifications can be introduced to geopolymeric cements
and to the process described above, by workers in the field, while
remaining within the terms of the invention.
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